Diamond I prototype JA8248, preserved at the Aichi Museum of Flight in Japan. · Alan Wilson, CC BY-SA 2.0, via Wikimedia Commons
Mitsubishi · Light Jet
Diamond I (MU-300)
The first production version of the Mitsubishi design that became the Beechjet 400 and Hawker 400.
A lot of jet for the money: a wider, taller cabin than an early Citation and a faster cruise. The catch is ownership. Two pilots, thirsty engines, scarce Mitsubishi-only parts and big overhaul bills can cost more each year than the jet itself.
Buy it if
You want the most cabin and speed per dollar in a two-pilot jet, fly mostly from runways of 5,000 ft or longer, and have a Beechjet-savvy shop and cash set aside for engine overhauls.
Skip it if
You need predictable costs, easy resale, hot-and-high airports or single-pilot flying. A Beechjet 400A or Citation II costs more to buy but is far easier to support, insure and sell.
Biggest compromise
Each engine overhaul can run $250,000–$575,000, which can exceed what the whole airplane is worth. With no factory pay-per-hour plan for these engines, a jet near its 3,500-hour overhaul point is worth far less than one with fresh engines, and parts unique to Mitsubishi-built airframes often come from salvaged aircraft.
The numbers that matter
Purchase price
$250K–$400K
guide value (Quantum Jets 2026 buyer's guide; PlanePhD)
What it costs per year
$1.3M
at 300 hrs · two professional pilots
How far it flies
1,510 nm
About 1,100 nm with four passengers and standard IFR reserves (our estimate)
How fast
400 kt
high-speed cruise
Seats
7
7 typical, up to 8
Pilots needed
2
Requires two pilots; the captain needs an MU-300 type rating.
Price
What one costs to buy
Guide value
$250K–$400K
Other sites
Priced vs call
with a price / call for price
No airworthy Diamond I is publicly listed right now. Published 2026 estimates put values around $250,000–$400,000; engine times drive the price.
Price vs its family and alternatives
Scroll to explore · select a jet for details
Diamond I (MU-300) · This aircraft
$250K–$400K guide
Guide value, not a listed asking price.
The least expensive here; next up is the Diamond IA (MU-300).
For sale now
None listed right now
Cost to own
What it costs per year to run
300hours / year
Per year
Per flight hour
Estimate — your operator will quote actual numbers.
Fuel, airframe maintenance, engine overhaul reserve and landing, handling, crew travel and miscellaneous rise as you fly more. Two professional pilots, recurrent training, two pilots, hangar, insurance and management stay the same however much you fly.
Where the money goes
- Two professional pilots$345,00027%
- Recurrent training, two pilots$37,5383%
- Hangar$28,4432%
- Insurance$24,0862%
- Management$24,0002%
- Fuel$447,81635%
- Airframe maintenance$171,60013%
- Engine overhaul reserve$119,4009%
- Landing, handling, crew travel and miscellaneous$97,5008%
Fuel is the biggest single cost at 35% of the total.
The JetGrade
64 out of 100 — Below its class average
Peer group: Cessna Citation I (500), Cessna Citation II (550), Learjet 25, Beechcraft Beechjet 400, Mitsubishi Diamond IA
Seven categories at a glance
- - - 70 = typical— This aircraft
Strongest on cabin & passenger comfort, weakest on reliability & support.
Grades are editorial opinions about the model, not any specific aircraft. Sponsors and affiliates have no input. Reviewed 2026-09-29.
Where it flies
Sample trips and reach
Typical trips on a map
Nonstop
Depends on weight or weather
Fuel stop likely
3 of 6 sample trips are comfortable nonstops.
Sample flight times
- 1.0 hr
Carlsbad → Las Vegas
205 nm · Short hop; keep loads light from Carlsbad
- 2.1 hr
Carlsbad → Aspen
625 nm · Hot-and-high; depends on weight and weather
- 2.4 hr
Santa Ana → San José del Cabo
765 nm · Nonstop with four passengers aboard
- 2.8 hr
Teterboro → West Palm Beach
900 nm · Nonstop with four passengers aboard
- 3.6 hr
Dallas → Teterboro
1,190 nm · Near its range limit; winds and load decide
- 6.5 hr
Carlsbad → Teterboro
2,100 nm · Needs one stop, typically mid-continent
Lineage
What came before and after
1982–1984
Mitsubishi Diamond I (MU-300)
Original Mitsubishi design with 2,500-lb-thrust engines and a 41,000-ft ceiling.
1985
Mitsubishi Diamond II (MU-300-10)
More powerful engines, more fuel and thrust reversers; only 11 built.
Size and cabin
How big it is, inside and out
Outside
Silhouette · scaled to length
Length
Wingspan
Height
Inside the cabin
Cabin length
Width
Height
Compare
How it stacks up
This aircraft
Diamond I (MU-300)
- JetGrade
- 64
- Price
- $250K–$400K guide
- Cost per year
- $1.3M
- Range
- 1,510 nm
- Speed
- 400 kt
- Seats
- 7
- Cabin length
- 15′ 6″
- Pilots
- 2
- Years built
- 1982–1984
After →
- JetGrade
- 61
- Price
- $361K–$361K guide
- Cost per year
- $1.26M
- Range
- 1,200 nm
- Speed
- 421 kt
- Seats
- 7
- Cabin length
- 15′ 6″
- Pilots
- 2
- Years built
- 1984–1985
Alternative
- JetGrade
- 68
- Price
- $1.2M
- Cost per year
- $1.33M
- Range
- 1,885 nm
- Speed
- 458 kt
- Seats
- 7
- Cabin length
- 15′ 7″
- Pilots
- 2
- Years built
- 1990–2003
Alternative
- JetGrade
- 67
- Price
- $895K
- Cost per year
- $919K
- Range
- 1,159 nm
- Speed
- 355 kt
- Seats
- 6
- Cabin length
- 15′ 9″
- Pilots
- 2
- Years built
- 1978–1994
- Beechcraft Beechjet 400A instead: The same family grown up: more thrust, more fuel, a double-club cabin and far broader parts and training support, for a higher purchase price.
- Mitsubishi Diamond IA instead: The same airframe with engine and system updates that fix much of the Diamond I's hot-day takeoff weakness.
- Cessna Citation II (550) instead: Slower, but a huge fleet, deep Textron support and better short-runway manners make it easier to own, maintain and resell.
Gold marks the best figure in each row.
Owning one
What to know before you buy
Engines & inspections
2 × Pratt & Whitney Canada JT15D-4 or JT15D-4D · 2,500 lbf each
No APUEngine hours until overhaul
- Engine mount bracket check · 200 hr
- Bleed-air bellows check · 400 hr
- Engine hot section · 1,750 hr
- Pitch trim actuator replacement · 1,800 hr
- Horizontal stabilizer rib inspection · 2,400 hr
- Engine overhaul · 3,500 hr
There is no factory pay-per-hour plan for these engines. Owners fund overhauls themselves, and third-party programs can extend overhaul intervals on condition.
Known issues
Engine overhaul exposure
Overhauls every 3,500 hours cost $250,000–$575,000 per engine, often more than the airplane is worth.
Scarce Mitsubishi-only parts
Mitsubishi left in 1985; shared parts come via Textron, unique ones often from salvaged airframes.
RVSM status varies
Without RVSM approval the jet cannot fly 29,000–41,000 ft; some listings only claim readiness.
Pre-buy checklist
0 of 10 checked
Textron Aviation service centers and independent Beechjet shops maintain the Diamond, and major overhaul shops such as StandardAero support its engines. Parts unique to Mitsubishi-built aircraft are scarce and often come from salvaged airframes.
Review
The full review
Strengths
- Flat-floor cabin 1.50 m (4 ft 11 in) wide and 4.72 m long, roomier than a Citation I of its era.
- Cruises at about 400 knots at 39,000 ft, well ahead of 1980s straight-wing Citations.
- Typically valued around $250,000–$400,000, a low entry price for a seven-seat jet with an aft lavatory.
Limitations
- Burns roughly 200 gallons an hour, about $1,500 an hour in fuel at September 2026 US prices.
- Weak hot-day takeoff performance; runways shorter than 5,000 ft are a poor fit on warm days.
- Only about 62 were built and Mitsubishi left the market in 1985, so some parts are scarce.
The Diamond I is the aircraft that started a family. Mitsubishi Heavy Industries designed it in Japan, flew it for the first time in August 1978 and won US certification in November 1981. Aircraft were finished in San Angelo, Texas, and deliveries began in July 1982. About 62 were built before the improved Diamond IA took over in 1984. Beech bought the design in 1985, and it lives on as the Beechjet 400, Beechjet 400A, Hawker 400XP and today's re-engined Hawker 400XPR and Nextant 400XTi.
Pilot's take
In the air the Diamond feels more modern than its 1980s Citation contemporaries: a swept wing, a roomy flat-floor cabin and a cruise near 400 knots. On the ground and in the climb it asks more of the crew. It is heavy for its 2,500-lb-thrust engines, so hot days and shorter runways need careful performance planning, and the climb slows noticeably above 30,000 ft. Roll control through spoilers, icing procedures added over the years and a type rating shared with the Beechjet all point to one conclusion: a crew already current in the Beechjet world is the best fit.
Who this is for
An experienced operator or small company with two type-rated pilots and a Beechjet-savvy shop, flying 300- to 1,000-nm trips with four to six people, who values cabin and speed over resale and budget certainty.
Ask about this aircraft
Answers come only from our research file on the Diamond I (MU-300).
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